"Open the book to page ninety-nine and read, and the quality of the whole will be revealed to you."
--Ford Madox Ford

Thursday, March 12, 2009

G. Cochran & H. Harpending's "The 10,000 Year Explosion"

Henry Harpending holds the Thomas Chair as Distinguished Professor in the Department of Anthropology at the University of Utah. A field anthropologist and population geneticist, he helped develop the “Out of Africa” theory of human origins. Gregory Cochran is a physicist and Adjunct Professor of Anthropology at the University of Utah.

Our book, The 10,000 Year Explosion, is about recent human evolution, mainly since the end of the last ice age about ten thousand years ago. Now the question is whether the book is holographic: if you look hard at a randomly picked page, say page 99, can you know what kind of book this is? Sounds tough, but as we understand it, we can now learn a lot about the fundamental rules of the world just by carefully examining a grain of sand... so let's take a stab at it.

On that page we talk about recent and ongoing changes in the dystrophin complex, a set of genes that function in both muscle and brain. We strongly suspect that humans have become weaker over the last 100,000 years, judging from the trend towards lighter skeletons, and we certainly hope that they have become smarter over that period. There would not have to be a tradeoff between brain and brawn - it's not dictated by the laws of physics, at least not strongly so - but the details of biochemistry and development can create such tradeoffs. The comparison between this path-dependent tradeoff with inevitable ones such as that between size and agility is not explicit in the text but we were thinking it and you should too. That's representative: there are many important points in this book that are implicit - never stated at all, and left as an exercise for the reader.

We also talk about recent changes in genes that affect hearing. New versions of those genes have been spreading over the past few tens of thousands of years, and some of the most recent ones are regional. We think that these changes must be related to changes in human language; they suggest that true speech hasn't been around all that long. There may even have been some adaptation to different languages. This is congruent with our main message: natural selection created and continues to shape all human traits, including those we consider the very essence of humanity, such as the ability to talk yourself out of a traffic ticket.